Using Singleton Pattern to Retain Previous Variable Values?

Is it possible using ExtendScript to retain the previous value of a property even after it has been updated by the user? I know after effects expressions update every frame, but I believe script values should be able to to persist. Is this sort of thing possible with ExtendScript?

I'm thinking something like this should be do-able using a singleton like pattern, but so far I have been unsuccessful. Heres what I've tried so far:

    var instance;

    //Check current instance value

    alert(getInstance().value);

    //Check if instance has a value, if not assign one, otherwise return current value

    function getInstance(){

        if(!instance){

            instance = createInstance();

        }

        return instance;

    }//End getInstance

   //Create new object with a value and return it

   function createInstance() {

        var object = new Object(mySel.property("Effects").property("Transform").property(1));

        return object;

    }//End createInstance

Or, if singletons are the wrong approach is there any type of storage mechanism that can be called in ExtendScript to write values to?

Thanks!